Roll Cage Question

[anthony1k]

The roll cage of my most recent aquisistion sits a bit too low for my taste. I would like to raise it by about 1/2 inch all around. I was thinking of cutting where the tubes meet the floor plates and welding extra steel plates. Does anyone see a problem with this plan? TIA

[joeg]

No problem with the theory. In practice, however, it could get interesting with the fit of the rear bracing tubes.

[TomL]

I've done something similar when I redid a cage, but it involved raising the whole thing two inches (I slid in two inch box tubing instead of a half inch plate). But it was a LOT of work - it required replacing rear tubes and redoing forward braces among other things. I can't imagine a situation where it would be worthwhile to do all that work for just a 1/2" taller cage.

[Flyinglizard]

Email me and I'll show you the solution. I have it in my book. " I'll send you a piece

[anthony1k]

Thank you all for the responses. I should have been more specific. Actually extensive reinforcement work is being done to the cage. So since I'm at it, I might as well try to raise it.

Flyinglizard you have mail.

[timo944]

Actually I have to disagree. This is a problem. First, what is the date of the logbook? If it is later than 1/1/2008, then the current rule 9.4.E.3.a. applies:
"Mounting plates welded to the structure of the car shall

not be less than .080 inches thick nor more than 0.25
inches thick. The maximum area of each mounting plate in
the American Sedan, Improved Touring, Showroom Stock,
Spec Miata, and Touring classes shall be 144 square
inches. Plates may be on multiple planes but shall not be
greater than 15 inches on any side."

If it is before that it's a bit challenging, because the GCR refers you to appendix I that has no specific rule for IT cars., so you may need to refer to Appendix I,

9.4.7. APPENDAGES

The following procedures are approved for modification to roll bars/cages
that do not meet the two (2) inch required minimum: The old main hoop
may be cut off near the chassis mounting and a new main hoop of equal
tube size or a section of equal tubing size may be added, and inner tube(s)
must be used to mate all sections together. All braces must be minimum
distance from top of hoop per Section 9.4. All welding for this modification
must be arc welded (min.). The inner tube(s) must be rosette welded
three (3) places near top and bottom, see figure 21.

I'd like to hear thoughts on this since I am in the exact same position as you are. So far, I have been happy to keep my head rested against the roll hoop while driving, even if the world is tilted a little to the left.

[Chip42]

2007 roll cage rules - appendix I of the 2010 GCR, 9.4.2.H: (IT used SS rules)


H. Mounting Plates:
1. Each mounting plate shall be at least .080 thick if welded and
3/16” thick (with appropriate backing plates) if bolted. There
shall be a minimum of three (3) bolts per mounting plate if
bolted.
2. Each mounting plate shall not be greater than 100 square
inches and shall be no greater than twelve (12) inches or less
than two (2) inches on a side.
3. Whenever possible, mounting plates shall extend onto a vertical
section of the structure (such as a rocker box).
4. The mounting plate may be multi-angled but must not exceed
these dimensions in a flat plane.
5. Any number of tubes may attach to the plate or each other.

the rule for "appendages" is actually only allowed if an open cockpit car does not pass the 2" rule of helmet clearance, though I'm sure it's been allowed on low cages in tin-tops.

of course - you can just build your cage or rebuild it to the new rules, if you are worried about it, have the scrutineer make a note in your logbook at the first annual after the work is completed. generally speaking, the old rules are published so that an existing car can be judged against the rules it was built to and grandfathered with in case it does NOT agree with the most current rules.
so meet the new and don't worry about the old.

[Flyinglizard]

I am in the process of getting the "crush boxes" approved and recommended. MM

[Chip42]

I am in the process of getting the "crush boxes" approved and recommended. MM

there's a lot of variables that will make the construction of boxes more or less safe - shape, welds, wall thicknesses, where on the chassis they are attached and the design of the stress paths that we may or may not have any way of predicting, etc..

have you had any feedback from the CRB or whomever and could you share the details of your request?

I've always liked the idea of boxes under the cage feet to allow for good, complete welds at the joints, but worried about the integrity of said boxes, their attachment to the chassis, etc.. particularly within the relatively limited surface area of 144sq in maximum. good rules can make these safer accross the board. as it is, they are relatively common and not well regulated (0.080" wall thickness boxes are techincally legal now and a very poor decision in my mind) so while some might be stellar, no 2 boxes are the same.

[joeg]

New or old rules I think you can box the feet to raise it. Under the old rules, you need to make certain that the box is welded to a vertical structure and not just sitting on floor shheetmetal.

Multiplanes are expressly allowed under the new rules, but you should still tie it into a vertical structure.

Boxing beats messing with a plugged tube extension, although done properly, that is very safe.

[Flyinglizard]

My "crush box" design is to spread the load to the other legs, by allowing the fix point to deflect some. The riser is designed to controlled crush about 7/8in before bottoming out and maxing the load on the floor.
This is more for the bolt in cages than the "welded to the rocker" cage.
This reduces punch through. HTH. MM

[Chip42]

New or old rules I think you can box the feet to raise it. Under the old rules, you need to make certain that the box is welded to a vertical structure and not just sitting on floor shheetmetal.

Multiplanes are expressly allowed under the new rules, but you should still tie it into a vertical structure.

Boxing beats messing with a plugged tube extension, although done properly, that is very safe.

box feet are decidedly legal, but not specifically addressed i the rules, new or old. my concerns are only that there are no well researched rules stating requirements of construction of such a device - if they fail, be it side impact or roll over, the results could be WORSE than being in a car without a cage. same holds true for traditional mounting to plates along existing surfaces, thus the vertical surface rules. the potential for movement is just greater with a box that fails.

I don't want to see them made illegal, particularly in light of the many cars about that have them already and advantages they can bring to overall cage integrity. I just want to see some sensible rules regarding their construction that go over and above the multi-plane and max surface area / linear dimension / plate thickness dimensional limits, as these are all associated with "traditional" building techniques and in no way specifically allow or describe the particular requirements for a boxed foot. the current wording is adequate to claim them as legal, and inadequate to ensure their safe construction.